Canada's Wonderland (the only Cedar Fair property in Canada) is the most attended seasonal theme park in North America (and one of the most profitable as well). It will not disappear for a very long time, given that fact.
La Ronde (the only Six Flags property in Canada) in Montreal is a very short free shuttle bus ride from Jean-Drapeau Metro station (and a substantial number of visitors to La Ronde arrive by public transit).
If the Spadina line were to be extended, then it would bring many visitors from Toronto to Wonderland (given that it currently costs extra to go to Wonderland from the TTC, as the 165 Weston Rd. North bus crosses Steeles Avenue (and the 60 Wonderland Express Bus operated by GO Transit is much faster, but slightly more expensive)). However, this extension will require much more funds (and political will) to do so.
But LaRonde is a bit different though. Because it's on an island, there's limited parking spaces, so they need those shuttle buses in order to ensure viability. Wonderland has the 400 and a sea of parking, so it doesn't need rapid transit (or even transit in general).
From my perspective, there are 3 ways Wonderland can financially benefit from an RT extension into the area:
1) The number of new visitors offsets or more than offsets the lost revenue from parking. Parking is currently $15, with a single-time park admission fee of $40. So if 8 people who normally drive (ignore multiple people in the same vehicle, just for the simplicity of the math) choose to take transit instead, you'd need 3 new people who wouldn't have gone to Wonderland otherwise in order for them to make the same amount of money. Given that a lot of trips to Wonderland are families who take 1 car, it should be easy for them to break even or even turn a profit when it comes to attracting new visitors compared to the status quo. I can see a lot of Toronto families taking advantage of that, especially with a TTC Day Pass that can take basically the entire family for $10 (I think it's still $10, may be a bit more than that now, but still, cheaper than parking).
2) Renting out parts of their parking lot to the TTC/Metrolinx (or charging on their own independent of the TTC/Metrolinx) as a Park N Ride lot. Most of the Park N Ride usage is weekdays, and Wonderland does their highest business on weekends during the summer, when demand for Park N Ride will be near zero.
3) Sell off or lease portions of their land to developers.
So could this be financially viable for them? Sure. Would it be a wise investment for Metrolinx? Hell no, at least not right now.
